Recovery of lead and indium from glass, primarily from electronic waste material

ABSTRACT

Lead and/or Indium cam be recovered from cullet containing indium and/or lead, such as cullet from CRTs and flat panel displays. A chloride salt melt including AlCl3 is used to dissolve the cullet. The melt may be electrolyzed and the lead and/or indium and other metals may be selectively electro-deposited from the salt melt. The two steps may be combined in a continuous process. The salts in the salt melt are not consumed but can be recycled, with exception of the flux due to formation of chlorine gas and alumina. It is also possible to recover lead and/or indium and other metals from the salt melt by vaporizing the respective chlorides and condensing them, or by leaching the salt phase in water and extracting the metals as hydroxides by hydrometallurgy methods.

TECHNICAL FIELD

The present invention relates to a process for recovering lead and/orindium from glass containing PbO and/or indium oxide, primarily fromelectronic waste material.

BACKGROUND ART

Lead is used in radiation shielding glasses in order to absorb gammaradiation and X-rays, e.g. in the cathode ray tubes, CRTs, used incomputer screens and television sets, where lowering the exposure of theviewers to soft X-rays is of concern.

Modern CRTs have a front panel made of essentially lead-free glass,there behind a funnel made from leaded glass, and at the far end a neckof highly leaded glass. These CRTs represent an environmental hazard ifdisposed improperly. In October 2001, the United States EnvironmentalProtection Agency created rules stating that CRTs must be brought tospecial recycling facilities. In November 2002, the EPA began finingcompanies that disposed of CRTs through landfills or incineration.Regulatory agencies, local and statewide, monitor the disposal of CRTsand other computer equipment. In Europe, disposal of CRT televisions andmonitors is covered by the WEEE Directive 2002/96/EC.

CRT monitors make up about 6% of the electronic waste in Europe, andapproximately 450,000 tons of cathode ray tube monitors are disposed ofin Europe every year. 70% of all the CRT monitors are dumped inlandfills or exported to the foreign countries, since no effectiverecycling systems are available. As indicated, CRT screens are becominga bigger problem especially in countries that manufactures thesemonitors, such as Japan, USA and Taiwan. Many countries handle the CRTwaste by sending it to lesser developed countries in exchange for moneyto avoid regulation protocols. However, this is a temporary solution, asnew techniques are being developed to find more effective ways toextract the lead and other hazardous components to be separated from theglass. The rest of said 70% of CRT monitors contain 33,300 tons of leadoxides. Calculated as pure lead, about 31,000 tons of lead isbeing-dumped in landfills annually in Europe.

The main concern with the dumping of CRT screens is the leaching of leadfrom the glasses. The leached lead is dangerous both for human beingsand environment. Dumping of CRT screens mostly occurs in developingcountries. This is a big problem, since it is very common for homelesspeople, both adults and children, to live in, and around refuse dumps.These people are therefore very exposed to the lead that is leached fromscreens by the rainwater. Many people who live around refuse dumpstherefore become lead poisoned by constant exposure. The most common wayfor the exposed people to become lead poisoned is that they are drinkingwater with high content of lead. Lead can also be spread to landsthrough the air, by mining and by direct discharges in water and lands.It takes a very long time for lead to form harmless compounds in thenature. A big problem is when lead is spread to farms and arable lands.When this happens, people are exposed to lead poisoning from eating thefruits and vegetables that are grown on these lands. Adults and childrencan also be affected when they eat meat from animals that has grazed ongrounds exposed to lead, and also when they eat fish, which is affectedby lead that comes from discharges from industries in seas and lakes,leachate from refuse dumps and landfills and outflow from sewages. Nosafe threshold for lead exposure has been discovered—i.e., there is noknown amount of lead that is too small to cause the body harm.

Studies of shredding cathode ray tube glass into cullet (small glasspieces) and reusing them for cathode ray tubes have been made byAssociation for Electric Home Appliances. Of these studies, a system ofextracting a cathode ray tube from a television main body and shreddingthe cathode ray tube into glass cullet has been developed (see“Electrotechnology”, January, 1997, for example).

A method of recovering glass as cullet is disclosed in, e.g., JapaneseLaid-Open Patent Application No. 61-50688. There is also known a methodof shredding cathode ray tube glass into cullet (small glass pieces) andreusing them for cathode ray tubes (e.g., Japanese Laid-Open PatentApplication No. 9-193762). A method of separating a cathode ray tubeinto a face plate and funnel in accordance with materials, and shreddingthem into cullet is disclosed in, e.g., Japanese Laid-Open PatentApplication No. 05-185064. Further, a method of separating a cathode raytube into a face plate and funnel, peeling fluorescent substances and ablack mask from the face plate, and recycling the face place isdisclosed in Japanese Laid-Open Patent Application No. 7-037509.

To reuse cathode ray tube glass, the glass must be separated into panelglass and lead-containing funnel glass. This is because, if lead ismixed in panel glass by a predetermined amount or more, a browningphenomenon occurs, and the lead-containing glass cannot be reused as araw material of the panel glass. For this reason, a cathode ray tube isseparated into a panel and funnel. For this purpose, there are proposeda method of defining a position to cut a cathode ray tube (JapaneseLaid-Open Patent Application No. 9-115449), and a method of melting fritglass, which joins a panel and funnel, thereby separating the panel andfunnel (Japanese Laid-Open Patent Application No. 7-45198).

WO 2009/139715 A1 discloses a process for chlorinating ore, slag, millscale, scrap, dust and other resources containing recoverable metalsfrom the groups 4-6, 8-12, and 14 in the periodic table. It is wellknown that metal values can be recovered from many sources such asscrap, ores and sea nodules by chlorination. The formed metal chloridescan subsequently be separated and extracted by fractional distillationand condensation, electrolysis of the salt or by hydrometallurgicalprocessing. However, to get a considerably higher reaction rate andyield of valuable metals than what is possible when ferric chlorideand/or cupric chloride are used as chlorine donors, aluminum chloride issubstituted for said chlorides.

Further, U.S. Pat. No. 4,853,094 discloses a process for the productionof metal Me (e.g. Sn) or an alloy containing metal Me from a metalhalide MeX_(n) (e.g. Sn Cl₄) by electrolysis in a cell having an anode,a liquid metal cathode comprising one or more metals M (e.g. liquid Zn)and a liquid electrolyte comprising a salt melt of one or more alkalimetal or alkaline earth metal halides (e.g. LiCl/KCl mixture). Theprocess comprises introducing metal halide MeX_(n), in which Merepresents a metal selected from the groups 2b, 3b (including thelanthanide series and the actinide series), 7b and 8 of the periodicsystem and Cr, Cu, Au, Ga, Sn, Pb and Bi, X represents halogen and nrepresents the valence of the metal Me, into the liquid metal cathodeand isolating Me or an alloy containing Me from the metal cathodematerial.

In Journal of Hazardous Materials 161(1109-1113) Issus 2/3 2009 a methodof recovering lead through a pyro vacuum process was suggested. However,as far as we know, no method that has been commercially accepted hasbeen proposed that solves the problem of rendering glass from scrappedCRT funnels harmless by recovering lead therefrom.

Another metal oxide that is desirable to recover from glass is Indium.Indium tin oxide (ITO) is one of the most widely used transparentconducting oxides and is e.g. used in flat panel displays such as LCD,LED, OLED, PDP etc, antistatic coatings, in light emitting diodes and invarious sources. Indium may also be present as indium doped zinc oxide.The price of indium is high and the supply is low. Hence there is a needof cost effective recycling of indium from glass present in electronicwaste material.

DESCRIPTION OF THE INVENTION

A main object of the present invention is to recover metal oxide, inparticular lead or indium, from glass containing PbO and/or indiumoxide, primarily from electronic waste material.

This object is achieved in accordance with the invention in that theprocess comprises:

-   -   a) crushing the glass to produce a cullet,    -   b) forming a mixture consisting of by weight % of the mixture;        -   60-95 of chloride salt composition consisting of at least            two metal chlorides selected from the group consisting of            alkali metal chlorides and alkaline earth metal chlorides,        -   5- 30 of AlCl₃, and        -   optionally 0-10 of halides, additional chlorides, sulfides            and/or oxides,    -   c) heating said mixture to form a salt melt,    -   d) dissolving the cullet in the salt melt,    -   e) recovering at least one of lead and indium from the salt        melt.

Thereby valuable metals can be recovered from glass as well as makingthe residue after the process essentially harmless. In regard to lead,it is possible to achieve a lead extraction ratio of more than 95%,which makes the residue after the process essentially harmless.

Preferably the amount of AlCl₃ is in the range of 5-20% by weight of themixture, more preferably 7-15 wt %, most preferably 8-13 wt %.

Preferably, the recovery of at least one of lead and indium from themelt includes:

-   -   electrolyzing the melt; and    -   selectively electrodepositing at least one of lead and indium.

By selective electro-deposition it is possible to recover most of theoxides present in the glass.

The temperature of the salt melt should preferably not exceed 1000° C.during the dissolution of the cullet, more preferably the temperatureshould not exceed 900° C., the suitable temperature being of the orderof at least 500° C. during the dissolution of the cullet and theelectrolysis of the melt. The upper limit is set by the fact that, athigher temperature some chlorides start evaporating from the melt. Thelower limit is decided by the liquidus temperature of the salt bath. Itis preferable to have the temperature of operation at least 100° C.above the liquidus temperature of the salt bath.

Graphite rods are suitably used for anode and cathode during theelectrolysis due to their inertness and low cost. When recovering lead,it is suitable that a pervious cathode diaphragm is provided around thecathode for collecting liquid lead. This is mainly to avoid thecontamination of the residue, which is nearly pure silica by liquidlead.

The cathode diaphragm suitably is made from alumina and has a pluralityof holes so that the liquid molten salt electrolyte can permeate throughthese holes while the solid residues can not pass through.

Preferably, a voltage of 2 to 3 V, more preferably 2.3-2.7 V, is usedfor extracting lead by electrolysis, as it was found to be favorable inthe preliminary trials. This is in conformity with cyclic voltamericstudies as well with graphite electrodes.

The melt is electrolyzed for a time suitably on the order of 2 to 8hours, preferably 3-6 hours.

Preferably, the weight ratio between flux and cutlet is on the order of0.25 up to 1.5, more preferably 0.3-1.0. For lead containing cullet mostpreferably 0.35-0.45. An increase of flux content and flux./cullet ratioseems not to contribute of extraction ratio of lead oxide since lowratios of flux content and flux/cullet already show very high extractionratio.

Preferably, the temperature is held for a time on the order of for 4-8hours during the dissolution step. Then the cullet will be softened andthe lead and/or indium value is extracted into the salt melt.

It is possible to vaporize metal chlorides from the melt and condensingthem for subsequent recovery of the metals of the condensed chlorides.The metal chlorides from the melt may also be recovered by leaching inwater and extracted to recover the metals as hydroxides by ahydrometallurgical method.

After recovering the lead and/or indium and optionally other metalspresent in the cullet, the chloride salts of the melt may be recycled.

After recovering lead and indium and possibly other metals from glass, aprocessing residue consisting essentially of Al₂O₃ and SiO₂ remains,which is useful for landfill, building construction, or as a rawmaterial for refractory industry.

Lead containing glass primarily comes from a funnel-shaped part and/or aneck part of a cathode ray tube of a computer screen or a televisionset.

Alternatively, the at least one of lead and indium can be recovered by aprocess using a liquid aluminum anode. In this process AlCl₃ isgenerated by an in situ formation during the electrolysis. This processincludes the steps of:

-   -   a) crushing the glass to produce a cullet,    -   b) providing a crucible containing a chloride salt melt, at        least one cathode and an anode connected to the salt melt,        heating means for heating the salt melt, and an aluminum melt        present at the bottom of the crucible, said aluminum melt        forming the anode or a part of the anode,    -   c) providing an initiating chlorine donor to the salt melt for        starting the reactions in the salt melt, said initiating        chloride donor being aluminum chloride and/or at least one metal        chloride that can be electrolyzed in step g) to form aluminum        chloride,    -   d) holding the temperature of the salt melt and the temperature        of the aluminum melt at a temperature where both are in liquid        phase,    -   e) introducing said cullet into the liquid salt melt,    -   f) reacting the aluminum chloride as a chlorine donor with the        cullet to form at least one of lead chloride and indium chloride        being dissolved in the salt melt,    -   g) electrolyzing the salt melt and selectively depositing at        least one of lead and indium at the cathode, optionally using a        cathode bag, and in situ forming aluminum chloride at the        contact surface between the aluminum melt and the salt melt,    -   h) recovering at least one of lead and indium from the salt        melt.

Cullet

The cullet is prepared by crushing glass containing PbO and/or indiumoxide. PbO containing glass primarily comes from a funnel-shaped partand/or a neck part of a cathode ray tube of a computer screen or atelevision set. Indium oxide containing glass primarily comes from flatpanel displays coated with indium tin oxide. Preferably, glasscontaining PbO and glass containing indium oxide are separated, so thatthe cullet contains lead or indium. However, indium and lead from amixed cullet can be recovered by selective electrodepositing.

Salt Composition

Preferably the salt composition consists of at least two of the saltsselected from the group: NaCl, KCl, LiCl, and CaCl₂, preferably at leastthree of the salts selected from the group: NaCl, KCl, LiCl, and CaCl2.Preferably the composition is selected so that the salt composition hasa liquidus temperature below 700° C., preferably below 600° C., morepreferably below 500° C. For a given combination of salts, thecomposition is preferably chosen to be within 10% by weight from thelowest eutectic point of the salt combination, more preferably within 5%by weight, most preferably within 1% by weight. However, other contentsmay be used as long as the liquidus temperature of the salt combinationis at least 50° C. lower than the operating temperature duringelectrolyzing; preferably 100° C. lower than the operating temperature.

In a preferred embodiment the salt composition essentially consists ofby weight % of the salt composition, 3-20 NaCl, 30-70 KCl, 20-60 LiCl,preferably 5-15 NaCl, 40-60 KCl, 30-50 LiCl, more preferably 7-12 NaCl,45-55 KCl, 35-45 LiCl. Such salt composition can provide low liquidustemperatures (eutectic temperature around 350° C.), good electricalconductivity to a comparably low cost.

In an alternative embodiment the salt composition essentially consistsof by weight % of the salt composition, 10-50 NaCl, 2-20 KCl, 50-80CaCl₂ preferably 25-35 NaCl, 3-10 KCl, 60-75 CaCl₂.

In an another alternative embodiment the salt composition essentiallyconsists of by weight % of the salt composition, 5-20 NaCl, 20-40 LiCl,40-70 CaCl₂ preferably 7-15 NaCl, 25-35 LiCl, 50-60 CaCl₂.

In an another alternative embodiment the salt composition essentiallyconsists of by weight % of the salt composition, 35-65 KCl, 20-50 LiCl,5-20 CaCl2 preferably 45-55 KCl, 30-40 LiCl, 10-15 CaCl₂.

Dissolving

To dissolve the cullet, a mixture is preferably provided, which consistsof A) 60-95% by weight of the mixture of a chloride salt compositionconsisting of at least two metal chlorides selected from the groupconsisting of alkali metal chlorides and alkaline earth metal chlorides,B) 5-30% by weight of the mixture of AlCl₃, and C) optionally 0-10% byweight of the mixture of halides, additional chlorides, sulfides and/oroxides, for instance but not limited to: Cao, Li₂O, NaO, MgCl₂, BaCl₂.In the most preferred embodiment the salt composition consist of NaCl,KCl, and LiCl and having a composition around the lowest eutectic pointfor the NaCl—KCl—LiCl system. The mixture is heated to form a salt melt.The cullet can be added before heating the mixture or after the saltmelt has been formed. This mixture is heated in a refractory containerunder protective atmosphere, suitably argon, to form a melt. Theatmosphere may also be nitrogen. Furthermore, chlorine gas may bedadmixed to the nitrogen or argon atmosphere. To dissolve the cullet, themelt is kept at high temperature usually for a time between about 4 andabout 8 hours. As a rule, the amount of cullet is preferably such that aweight ratio flux/cullet is between about 0.25 and about 1.5, morepreferably 0.30-1.0, most preferably 0.35-0.45. The temperature shouldbe lower than 1000° C., more preferably lower than 900° C. Otherwiselead chloride may evaporate from the melt. For optimal economy thetemperature is preferably in the range of 550-700° C. during thedissolution of the cullet and the electrolysis of the melt, morepreferably 580-650° C.

For PbO the dissolving reaction is:

3PbO+2AlCl3→3PbCl₂+Al₂O₃  (1a)

A flux/cullet ratio of 0.37 appears to be sufficient to dissolve leadoxide in the salt melt.

For indium the dissolving reaction is:

In₂O₃+2AlCl₃→2InCl₃+Al₂O₃  (1b)

Since the aluminum chloride is difficult to recover after the extractionprocess, it is desirable that there is no excessive addition of aluminumchloride.

To recover at least one of lead and indium from the melt, variousprocesses that are known per se may be used. It is interesting to notethat the salt melt used for extraction can be recycled. The lead and/orindium as well as other metals can be selectively electro-deposited fromthe salt melt. However, it is also possible to use vaporization of themetal chlorides and condensing them, or leach the salt phase in waterand extracting the metals as hydroxides by hydrometallurgy method. Theprocess can be designed to be continuous by combining the two steps. Theanode off-gas from a subsequent electrolysis, Cl₂, can be reused foraccentuating the dissolution of slag/ores. The residue after processingglass consists essentially of Al₂O₃ and SiO₂ and can be used forlandfill, building construction or as a raw material for the refractoryindustry.

Electrolysis using conventional anode/s and cathode/s The electrolysispreferably is carried out in the refractory container that holds thesalt melt with the dissolved cullet, and the lead and/or indium andpossibly other metal is recovered as a cathode deposit.

In one embodiment lead is recovered from PbO containing glass. Twoelectrodes of graphite are immersed into the salt melt containingdissolved cullet and connectable to a DC source, which can deliver a DCcurrent at a voltage of 2 to 3 V, preferably 2.3-2.7 V, so that thefollowing reactions'occur with respect to lead.

2Cl⁻→Cl₂(g)+e ⁻  (2)

Pb²⁺+2e ⁻→Pb(l)  (3)

2Al³⁺+3O²⁻→Al₂O₃(s)  (4)

This is around 1 volt higher than the theoretical decomposition voltagefor PbCl₂ to compensate for polarization and other effects. The voltagechosen is low enough to avoid decomposition of AlCl₃. The decompositionof AlCl₃ in the electrolysis process also need an over-voltage inregards of the theoretical decomposition voltage of AlCl₃. In this case,2.4+1=3.4 V. Thus a voltage lower than 3 V avoids electrolyticdecomposition of AlCl₃.

Indium can be co-deposited with Sn when the indium oxide is indium tinoxide or thay may be selectively electrodeposited.

Preferably the batch of melt is electrolyzed for 2 to 8 hours. Duringthe electrolysis, the temperature is preferably held above 500° C., morepreferably about 600° C.

For collecting liquid lead, a pervious cathode bag may be providedaround the cathode. The cathode bag suitably is made from alumina andhas a plurality of holes, through which the ions can pass. The holes maybe cuts extending in the circumferential direction.

After recovering lead and/or indium and possibly other metals, thechloride salts of the melt may be recycled. Then, a processing residueconsisting essentially of Al₂O₃ and SiO₂ remains, which is useful forlandfill, building construction, or as a raw material for refractoryindustry. The lead containing glass processed in accordance with theinvention primarily comes from a funnel-shaped part and/or a neck partof a cathode ray tube of a computer screen or a television set.

Dissolving and Electrolysis Using Aluminium Anode

In an alternative embodiment, an aluminium melt form the anode or a partof the anode, for instance by immersing an electrode, e.g. a graphiteelectrode, in the aluminium melt and connecting it to positive polarityduring electrolysis. Alternatively, the crucible is at least partly madein a conductive material being in contact with the aluminium melt, andconnecting the crucible positive polarity during the electrolysis.Thereby, the crucible and the molten aluminium operate as an anode. Ofcourse at least one cathode is still required during electrolysis, e.g.one or more graphite electrode/s submerged in the salt melt voltage

When using an aluminium melt at the bottom of the crucible as the anodeor part of the anode, the salt melt and the aluminium are heated to atemperature where both are in liquid phase. To improve viscosity of thesalt melt, the temperature of the salt melt is preferably at least 50°C. above the liquidus temperature of the salt melt, more preferably atleast 100° C. above the liquidus temperature of the salt melt. Thetemperature should be at least 660° C. and not more than 1000° C.,preferably the temperature is in the range of 700-900° C.

During the electrolysis metals/s from metal chloride/s is deposited atthe cathode. At the contact surface between the salt melt and thealuminium melt chloride ions are reacting with aluminium, therebyforming AlCl₃. This means that during steady state the salt melt can bewholly or partly self-supporting in regards of AlCl₃ and also thatemission of chlorine gas is reduced. Lesser amounts of chlorine gas mayform even when using an aluminium melt as the anode or part of theanode. This gas may be recovered.

At the cathode metal/s are deposited in solid or liquid state formetal/s with lower melting point than the temperature of the salt melt.For collecting liquid metal, e.g. lead, a pervious cathode bag may beprovided around the cathode. The cathode bag suitably is made fromalumina and has a plurality of holes, through which the ions can pass.The holes may be cuts extending in the circumferential direction.

The composition of the salt melt is preferably the same as when using aconventional graphite anode/s.

An initiating chloride donor is provided to start the reactions in thesalt melt. The initiating chloride donor may be aluminium chlorideand/or at least one metal chloride that can be electrolyzed, i.e. sothat chloride ions forms AlCl₃ at the contact surface between the saltmelt and the aluminium melt.

In one embodiment, the initiating chloride donor includes a metalchloride of the same type as provided in the chloride salt composition,e.g. at least one metal chloride selected from the group consisting ofchlorides of Li, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, and Ra.

In a preferred embodiment, the initiating chloride donor includesaluminium chloride added to the mixture before heating it or to the saltmelt, said aluminium chloride being added up to 20% by weight of thesalt mixture, preferably 1-15% by weight, more preferably 5-10% byweight.

When using aluminium melt as the anode or part of the anode the stepsdissolving and recovering by electrolysis are expedited simultaneously,preferably for at least 2 hours.

As the indium and/or lead is deposited, additional cullet can bestepwise or continuously added to the salt melt. The electrolysis anddissolving operation can for instance be performed for 2-8 hours; whereafter metals deposited at the cathode/s is collected, and theelectrolysis can be restarted. To avoid interrupts of the electrolysis,another “clean” electrode can be submerged. Alternatively, the salt meltmay have a plurality of electrodes which one after the other isactivated as a cathode and while the former is deactivated. Thereby themetals can be selectively deposited at individual electrodes.

The residue after processing contains Al₂O₃ and other stable oxides suchas SiO₂.

Example of Recovery of Lead from CRT Monitor

A sample of CRT glass was supplied by East Japan Recycling SystemsCorporation (EJRS). The CRT monitors were taken apart, and some of theparts were recycled. The treatment of CRT monitors by EJRS is describedin the following.

The monitors were taken apart by hand, and the CRTs were separated.Printed boards, deflecting yokes, interconnections and speakers werealso taken and recycled. The separated CRTs were polished by a brushcleaning equipment, and excrescences on the surface of CRT were removed.Then the panel and funnel were separated by a P/F divider. Since theglass compositions of the panel and funnel are different, they have tobe recycled separately. The funnel glass was washed and dry-scrubbed toremove the paint of carbon and iron oxide on the surface of the glass,and then the funnel cullet was produced. This cullet is the raw materialof CRT glass.

As indicated above, the glass used in a CRT is of different kinds in thepanel, the funnel and the neck of a CRT. The panel contains abarium-strontium glass, the weight of which is about two-thirds of theCRT monitor's total weight. The funnel is made of leaded glass. Theweight of it is about one-third of the CRT monitor's total weight. Theneck is made out of a high lead content glass, which surrounds theelectron gun.

Two different analyses were made of the funnel cullet supplied weremade. The result of the analyses is shown in Table 1, where the twodifferent analyses are designated CRT 1 and CRT 2.

TABLE 1 Composition of the funnel glass (Weight %) Component ReferenceCRT 1 CRT 2 Na₂O 5~7 10.685 7.000 MgO 1~3 1.469 1.363 Al₂O₃ 3~5 2.1772.094 SiO₂ 50~53 59.250 60.950 K₂O 7~9 10.324 8.490 CaO 3~5 1.721 2.076FeO  0~0.1 0.156 0.156 SrO 0~1 0.459 0.445 ZrO₂ 0~1 0.022 0.020 Sb₂O₃0.1~0.5 0.057 0.057 BaO 0~1 0.580 0.564 PbO 21~24 20.316 18.787 Li₂O 0~10.017 0.017 TiO₂ 0.3~0.5 0.018 0.017 ZnO 0~1 0.237 0.240 Total 107.485102.275

The metal chlorides were supplied by Sigma-Aldrich, USA, and therefractory container was an alumina crucible (99.5%, 40 mm outerdiameter, 36 mm inner diameter, 60 mm height, from KERANOVA AB, Sweden)having a lid. The chloride salts (8% by weight of NaCL, 53% by weight ofKCL and 39% by weight of LiCl) and the cullet were mixed evenly, placedin the crucible and held for a predetermined time in an oven. Argon gas(ICP5.0, AGA gas AB, Sweden) was introduced from the bottom of thefurnace as protective gas. Graphite rods (diameter of 6 mm, Lorraine,Paris) were used as electrodes and iron rods (6 mm diameter) as leadwires.

During the dissolution process, the electrodes were held 2-4 cm abovethe salt melt. After the salt mixture was melted and held fordissolution at a fixed time, the electrodes were immersed in the saltmelt, and electrolysis started, supplied by DC power (HP Hewlett 6632A).After electrolysis, the electrodes were taken out from the salt melt,held above the salt melt and cooled down under the protection of argongas. The sample in the crucible was dissolved in the distilled watercompletely and filtrated. The residue was prepared for chemicalanalysis. ICP-AES analysis was applied for the elements Al, Fe, Sr, Zr,Sb, Ba, Zn, Pb, Li and Ti. Atomic absorption analysis was applied forthe elements Na, Mg, Ca and K. The deposition products on the cathodewere analyzed by Scanning Electron Microscope (SEM) (JSM-840, JEOL)equipped with Energy-Dispersive X-ray Spectrometry analysis (EDS link,Oxford).

Four factors, viz. holding temperature, holding time, flux content (moleratio to NaCl—KCl—LiCl mixture) and flux/cullet (weight ratio), wereinvestigated. The parameters varied during the tests were temperature(600, 800 and 1000° C.), holding time (4 and 8 hours), flux content (11,15, 19 and 29 wt %) and flux/cullet (0.37, 0.5, 0.7, 0.9 and 1.5) wereapplied. The extraction ratio of various metal oxides in the CRT glassin the salt melt is shown in Table 2. In this table, the extractionratio is defined as the ratio of remained oxides in residue versus theamount of corresponding oxides in the initial CRT glass.

TABLE 2 Extraction ratio of metal oxides in NaCl—KCl—LiCl systemExtraction ratio of metal oxides (%) Conditions No. Na₂O MgO Al₂O₃ K₂OCaO FeO SrO Sb₂O₃ BaO PbO Li₂O ZnO Temp Time Flux Flux/CRT 1 97.7 99.1−623 94.2 99.6 77.7 96.1 73.2 95.3 96.4 −1242 97.1 600° C. 4 h 11 wt %0.37 2 98.5 98.8 −122 95.5 99.6 67.7 95.7 84.0 95.6 95.0 −2471 91.2 0.73 97.7 99.1 −849 95.5 99.8 73.4 96.7 62.9 96.2 95.1 −1204 79.3 0.9 498.5 99.1 −219 93.6 99.8 49.4 93.8 76.8 93.8 94.9 −1755 91.7 15 wt %0.37 5 98.5 99.1 −768 96.2 99.4 70.0 95.8 67.0 95.5 96.0 −1724 95.1 0.76 97.7 99.1 −623 94.2 99.6 77.7 96.1 73.2 95.3 96.4 −1242 97.1 0.9 798.5 98.8 −122 95.5 99.6 67.7 95.7 84.0 95.6 95.0 −2471 91.2 19 wt %0.37 8 97.7 99.1 −849 95.5 99.8 73.4 96.7 62.9 96.2 95.1 −1204 79.3 0.79 98.5 97.7 −449 78.8 74.0 73.4 94.4 67.0 94.8 94.6 −1306 98.3 0.9 1087.0 94.2 −238 51.2 86.7 62.5 91.9 68.3 92.2. 93.4 −9537 93.5 29 wt %0.5 11 98.1 97.5 −352 95.4 94.2 28.1 92.2 66.9 92.5 93.3 −2459 89.0 8 h11 wt % 0.7 12 98.5 98.6 −673 97.9 96.9 64.0 96.9 66.6 96.7 96.8 −97296.6 19 wt % 13 98.5 98.5 −584 97.9 96.2 69.2 96.4 67.8 96.5 96.3 −113697.3 29 wt % 14 96.7 55.5 −868 85.7 98.1 81.7 72.0 14.4 69.8 60.8 −801890.6 800° C. 4 h 19 wt % 0.9 15 95.6 63.1 −1015 82.1 95.7 77.0 −4.3 9.471.6 64.9 −7340 92.8 1.5 16 97.3 37.4 −439 91.0 94.5 58.9 43.7 −111 42.551.9 −8398 88.7 29 wt % 17 96.6 42.0 −799 85.0 86.1 11.4 69.7 −4.0 66.553.3 −8322 90.1 8 h 19 wt % 0.9 18 94.4 76.0 −880 73.2 99.2 48.4 95.543.5 94.3 90.9 −5238 94.4 1000° C.  4 h

Two methods were used to estimate the amount of extracted oxides. First,the residue after dissolution was filtrated, and then subjected to twochemical analyses, viz. ICP-AES and atomic absorption analysis. Itshould be mentioned that this extraction ratio is not always equal tothe solubility in the salt melt. Some of the oxides can be evaporated aschlorides. Extraction ratio of aluminum and lithium oxide shows anegative value, which means that the amount of the oxide increased.Almost all of the oxides show very high extraction ratio, except ironand antimony oxide. However, iron and antimony oxide show an extractionratio of approximately 70%. Concerning lead oxide, the ratio is about50-60% at 800° C., and 91% at 1000° C. These values are lower than thatobtained at 600° C. In addition, increases of flux content andflux/cullet ratio appear not to contribute to increasing the extractionratio of lead oxide, since already low ratios of flux content andflux/cullet show very high extraction ratios. In the presentexperimental tests, a flux/cullet ratio of 0.37 appears to be sufficientto dissolve lead oxide in the salt melt. This value is the theoreticalamount to complete reaction (1) above.

The variation of lead oxide extraction ratio due to different processparameters was investigated. The extraction ratio of lead oxide at 600°C. was approximately 96% and did not depend on the holding time.Concerning variation with temperature, the extraction ratio was about95, 60 and 91% at 600, 800 and 1000° C., respectively. The ratio seemsto be random. However, it can be said that the high temperature did notcontribute to a rise of the extraction ratio. Further, high flux contentdid not give a significant change in the extraction ratio. Similarly, achange in the flux/cullet ratio did not result in any significant changeof the extraction ratio of lead oxide that was approximately 95%.Consequently, higher temperature, flux content and flux/CRT ratio,longer holding times are not needed. As mentioned above, already lowervalues of the parameters give high extraction ratios, and therefore anincrease of parameter values does not result in any a rise of theextraction ratio. Based on the results, the optimized process parameterswere chosen as-600° C. of temperature, 0.37 of flux/cullet, 4 hours ofholding time, and 11% by weight of flux content. In the test at 1000° C.the evaporation of AlCl₃ was high. It is therefore preferred to keep thetemperature lower than 1000° C., preferably lower than 900° C.

The dissolution test proves that the metal values in CRT glass can beextracted into the salt phase. Under different cell potentials, variousmetals or alloys can be deposited on the cathode surface. All of themetal chlorides in the melt have a theoretical decomposition voltage.The decomposition voltages of silicon chloride and lead chloride areclose to each other, which means that it is expected to be difficult todepose the two separated from each other. However, it is very difficultto dissolve silicon oxide in the salt melt, and thus silicontetrachloride does not practically exist in the melt. Consequently, itis possible to deposit lead selectively. It should be noted that theelectro-deposition of metals can be affected by a number of factors evenin pure molten salt system, as for example, over voltage, currentdensity, current efficiency, electro bath conductivity, the nature andsurface of the cathode material and distance between electrodes, etc.

In the experimental electrolysis process, 600° C. of temperature, 0.9 offlux/cullet, 4 hours of holding time and 19 wt % of flux content wereselected because of the small size of the crucible. Then, the amount ofCRT glass was 9.3 g, which contained approximately 1.8 g of lead oxide.If 100% of the lead oxide is dissolved in the salt melt and all of thelead is deposited, approximately 1.7 g of lead is recovered. This amountof lead is the available maximum value for a small crucible.

As demonstrated above, a salt extraction process has been developed forthe recovery of lead and other metals from CRT glass. According to theanalysis of CRT glass, the glass contains approximately 19% of leadoxide, and approximately 96% of lead oxide was extracted by thedissolution in the salt melt step. The optimized process parameters inthe dissolution step were (a) a temperature of 600° C., (b) a holdingtime of 4 hours, (c) a flux/cullet ratio of 0.37, and (d) a flux contentof 11 wt %. Several electrolysis tests were performed with the moltensalts and CRT glass. A voltage of 2.3 V was used to electro-depositlead. A liquid phase of lead was deposited and dropped from the cathodeinto a cathode bag, where it was collected.

INDUSTRIAL APPLICABILITY

The main concern with the dumping of cathode ray tube (CRT) screens isthe leaching of lead from the glasses. Lead is used in radiationshielding glasses in order to absorb gamma radiation and X-rays, e.g. inthe cathode ray tubes used in computer screens and television sets,where lowering the exposure of the viewers to soft X-rays is of concern.The leached lead is dangerous both for human beings and environment. Thepresent invention solves the problem of rendering glass from scrappedCRT funnels harmless by recovering lead therefrom. Lead and other metalsare present as oxides in the glass and are dissolved in a chloride saltmelt, from which they are recovered by electrolysis, for example. Theresidue after processing, which consists essentially of Al₂O₃ and SiO₂,can be used for landfill, building construction or as a raw material forthe refractory industry.

Similarly, indium can be recovered from indium tin oxide coated glass

1. A process, for recovering lead and/or indium from glass containingPbO and/or indium oxide, primarily from electronic waste material,comprising: f) crushing the glass to produce a cullet, g) forming amixture consisting of by weight % of the mixture; 60-95 of chloride saltcomposition consisting of at least two metal chlorides selected from thegroup consisting of alkali metal chlorides and alkaline earth metalchlorides, 5-30 of AlCl₃, and optionally 0-10 of halides, additionalchlorides, sulfides and/or oxides, h) heating said mixture to form asalt melt, i) dissolving the cullet in the salt melt, and j) recoveringat least one of lead and indium from the salt melt.
 2. The process asclaimed in claim 1, wherein the salt composition consists of at leasttwo of the salts selected from the group: NaCl, KCl, LiCl, CaCl₂.
 3. Theprocess as claimed in claim 1, wherein the salt composition essentiallyconsists of by weight % of the salt composition, 3-20 Na, 30-70 KCl,20-60 LiCl.
 4. The process as claimed in claim 1, wherein the saltcomposition essentially consists of by weight % of the salt composition,10-50 NaCl, 2-20 KCl, 50-80 CaCl₂.
 5. The process as claimed in claim 1,wherein the salt composition essentially consists of by weight % of thesalt composition, 5-20 NaCl, 20-40 LiCl, 40-70 CaCl₂.
 6. The process asclaimed in claim 1, wherein the salt composition essentially consists ofby weight % of the salt composition, 35-65 KCl, 20-50 LiCl, 5-20 CaCl₂.7. The process as claimed in any one of claim 1 or 6, wherein the amountof AlCl3 is in the range of 5-20% by weight of the mixture.
 8. Theprocess as claimed in claim 1, wherein the salt composition is selectedto have a liquidus temperature below 700° C.
 9. The process as claimedin claim 1, wherein a weight ratio between the flux and cullet is on theorder of 0.25 up to 1.5.
 10. The process as claimed in claim 1, furthercomprising holding the temperature for a time on the order of 4-8 hoursduring the dissolution step.
 11. The process as claimed in claim 1,wherein the recovery of at least one of lead and indium from the meltincludes: electrolyzing the melt; and selectively electrodepositing atleast one of lead and indium.
 12. The process as claimed in claim 11,further comprising holding the melt at a temperature of at least 500° C.during the dissolution of the cullet and the electrolysis of the meltand at most 900°.
 13. The process as claimed in claim 11, furthercomprising electrolyzing the melt for a time on the order of 2 to 8hours.
 14. The process as claimed in claim 1, further comprisingcollecting chlorine gas evolved during the electrolysis.
 15. The processas claimed in claim 1, further comprising vaporizing metal chloridesfrom the melt and condensing them for subsequent recovery of the metalsof the condensed chlorides.
 16. The process as claimed in claim 1,further comprising leaching metal chlorides from the melt in water andextracting the metals as hydroxides by a hydrometallurgical method. 17.The process as claimed in claim 1, further comprising recycling thechloride salts of the melt.
 18. The process as claimed in claim 1,further comprising recovering a processing residue consistingessentially of Al₂O₃ and SiO₂ and using it for landfill, buildingconstruction, or as a raw material for refractory industry.
 19. Theprocess as claimed in claim 1, wherein the glass contains PbO and comesfrom a funnel-shaped part and/or a neck part of a cathode ray tube of acomputer screen or a television set.
 20. A process for recovering leadand/or indium from glass containing PbO and/or indium oxide, primarilyfrom electronic waste material, said process including the steps of: i)crushing the glass to produce a cullet, j) providing a cruciblecontaining a chloride salt melt, at least one cathode and an anodeconnected to the salt melt, heating means for heating the salt melt, andan aluminum melt present at the bottom of the crucible, said aluminummelt forming the anode or a part of the anode, k) providing aninitiating chlorine donor to the salt melt for starting the reactions inthe salt melt, said initiating chloride donor being aluminum chlorideand/or at least one metal chloride that can be electrolyzed in step g)to form aluminum chloride, l) holding the temperature of the salt meltand the temperature of the aluminum melt at a temperature where both arein liquid phase, m) introducing said cullet into the liquid salt melt,n) reacting the aluminum chloride as a chlorine donor with the cullet toform at least one of lead chloride and indium chloride being dissolvedin the salt melt, o) electrolyzing the salt melt and selectivelydepositing at least one of lead and indium at the cathode, optionallyusing a cathode bag, and in situ forming aluminum chloride at thecontact surface between the aluminum melt and the salt melt, and p)recovering at least one of lead and indium from the salt melt.
 21. Theprocess according to claim 20 wherein the initiating chloride donorincludes aluminium chloride added to the mixture before heating it or tothe salt melt, said aluminium chloride being added up to 20% by weightof the chloride salt mixture.
 22. The process as claimed in claim 20,wherein the salt melt and the aluminium melt is held at a temperatureabove 660° C.
 23. The process as claimed in claim 20, wherein theprocess is partly or wholly self-supporting during steady state by thealuminum chloride formed during the electrolyzing.